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Macros

Detailed Description

The QByteArray class provides an array of bytes.

QByteArray can be used to store both raw bytes (including '\0's) and traditional 8-bit '\0'-terminated strings. Using QByteArray is much more convenient than using const char *. Behind the scenes, it always ensures that the data is followed by a '\0' terminator, and uses implicit sharing (copy-on-write) to reduce memory usage and avoid needless copying of data.

In addition to QByteArray, Qt also provides the QString class to store string data. For most purposes, QString is the class you want to use. It stores 16-bit Unicode characters, making it easy to store non-ASCII/non-Latin-1 characters in your application. Furthermore, QString is used throughout in the Qt API. The two main cases where QByteArray is appropriate are when you need to store raw binary data, and when memory conservation is critical (e.g., with Qt for Embedded Linux).

One way to initialize a QByteArray is simply to pass a const char * to its constructor. For example, the following code creates a byte array of size 5 containing the data "Hello":

QByteArray ba("Hello");

Although the size() is 5, the byte array also maintains an extra '\0' character at the end so that if a function is used that asks for a pointer to the underlying data (e.g. a call to data()), the data pointed to is guaranteed to be '\0'-terminated.

QByteArray makes a deep copy of the const char * data, so you can modify it later without experiencing side effects. (If for performance reasons you don't want to take a deep copy of the character data, use QByteArray::fromRawData() instead.)

Another approach is to set the size of the array using resize() and to initialize the data byte per byte. QByteArray uses 0-based indexes, just like C++ arrays. To access the byte at a particular index position, you can use operator[](). On non-const byte arrays, operator[]() returns a reference to a byte that can be used on the left side of an assignment. For example:

A QByteArray can embed '\0' bytes. The size() function always returns the size of the whole array, including embedded '\0' bytes. If you want to obtain the length of the data up to and excluding the first '\0' character, call qstrlen() on the byte array.

After a call to resize(), newly allocated bytes have undefined values. To set all the bytes to a particular value, call fill().

To obtain a pointer to the actual character data, call data() or constData(). These functions return a pointer to the beginning of the data. The pointer is guaranteed to remain valid until a non-const function is called on the QByteArray. It is also guaranteed that the data ends with a '\0' byte unless the QByteArray was created from a raw data. This '\0' byte is automatically provided by QByteArray and is not counted in size().

The replace() and remove() functions' first two arguments are the position from which to start erasing and the number of bytes that should be erased.

When you append() data to a non-empty array, the array will be reallocated and the new data copied to it. You can avoid this behavior by calling reserve(), which preallocates a certain amount of memory. You can also call capacity() to find out how much memory QByteArray actually allocated. Data appended to an empty array is not copied.

A frequent requirement is to remove whitespace characters from a byte array ('\n', '\t', ' ', etc.). If you want to remove whitespace from both ends of a QByteArray, use trimmed(). If you want to remove whitespace from both ends and replace multiple consecutive whitespaces with a single space character within the byte array, use simplified().

If you want to find all occurrences of a particular character or substring in a QByteArray, use indexOf() or lastIndexOf(). The former searches forward starting from a given index position, the latter searches backward. Both return the index position of the character or substring if they find it; otherwise, they return -1. For example, here's a typical loop that finds all occurrences of a particular substring:

If you simply want to check whether a QByteArray contains a particular character or substring, use contains(). If you want to find out how many times a particular character or substring occurs in the byte array, use count(). If you want to replace all occurrences of a particular value with another, use one of the two-parameter replace() overloads.

QByteArrays can be compared using overloaded operators such as operator<(), operator<=(), operator==(), operator>=(), and so on. The comparison is based exclusively on the numeric values of the characters and is very fast, but is not what a human would expect. QString::localeAwareCompare() is a better choice for sorting user-interface strings.

For historical reasons, QByteArray distinguishes between a null byte array and an empty byte array. A null byte array is a byte array that is initialized using QByteArray's default constructor or by passing (const char *)0 to the constructor. An empty byte array is any byte array with size 0. A null byte array is always empty, but an empty byte array isn't necessarily null:

All functions except isNull() treat null byte arrays the same as empty byte arrays. For example, data() returns a pointer to a '\0' character for a null byte array (not a null pointer), and QByteArray() compares equal to QByteArray(""). We recommend that you always use isEmpty() and avoid isNull().

Notes on Locale

Number-String Conversions

Functions that perform conversions between numeric data types and strings are performed in the C locale, irrespective of the user's locale settings. Use QString to perform locale-aware conversions between numbers and strings.

8-bit Character Comparisons

In QByteArray, the notion of uppercase and lowercase and of which character is greater than or less than another character is locale dependent. This affects functions that support a case insensitive option or that compare or lowercase or uppercase their arguments. Case insensitive operations and comparisons will be accurate if both strings contain only ASCII characters. (If $LC_CTYPE is set, most Unix systems do "the right thing".) Functions that this affects include contains(), indexOf(), lastIndexOf(), operator<(), operator<=(), operator>(), operator>=(), toLower() and toUpper().

This issue does not apply to QStrings since they represent characters using Unicode.

QByteArray::QByteArray ( intsize, charch )

QByteArray::QByteArray ( const QByteArray & other )

Constructs a copy of other.

This operation takes constant time, because QByteArray is implicitly shared. This makes returning a QByteArray from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), taking linear time.

QByteArray & QByteArray::append ( const QByteArray & ba )

Note: QByteArray is an implicitly shared class. Consequently, if this is an empty QByteArray, then this will just share the data held in ba. In this case, no copying of data is done, taking constant time. If a shared instance is modified, it will be copied (copy-on-write), taking linear time.

If this is not an empty QByteArray, a deep copy of the data is performed, taking linear time.

This operation typically does not suffer from allocation overhead, because QByteArray preallocates extra space at the end of the data so that it may grow without reallocating for each append operation.

Appends the string str to this byte array. The Unicode data is converted into 8-bit characters using QString::toAscii().

If the QString contains non-ASCII Unicode characters, using this function can lead to loss of information. You can disable this function by defining QT_NO_CAST_TO_ASCII when you compile your applications. You then need to call QString::toAscii() (or QString::toLatin1() or QString::toUtf8() or QString::toLocal8Bit()) explicitly if you want to convert the data to const char *.

QByteArray & QByteArray::append ( const char * str )

This is an overloaded function.

Appends the string str to this byte array.

QByteArray & QByteArray::append ( const char * str, intlen )

Appends the first len characters of the string str to this byte array and returns a reference to this byte array.

If len is negative, the length of the string will be determined automatically using qstrlen(). If len is zero or str is null, nothing is appended to the byte array. Ensure that len is not longer than str.

QByteArray & QByteArray::append ( charch )

This is an overloaded function.

Appends the character ch to this byte array.

char QByteArray::at ( inti ) const

Returns the character at index position i in the byte array.

i must be a valid index position in the byte array (i.e., 0 <= i < size()).

int QByteArray::capacity () const

Returns the maximum number of bytes that can be stored in the byte array without forcing a reallocation.

The sole purpose of this function is to provide a means of fine tuning QByteArray's memory usage. In general, you will rarely ever need to call this function. If you want to know how many bytes are in the byte array, call size().

void QByteArray::clear ()

const char * QByteArray::constData () const

Returns a pointer to the data stored in the byte array. The pointer can be used to access the bytes that compose the array. The data is '\0'-terminated unless the QByteArray object was created from raw data. The pointer remains valid as long as the byte array isn't reallocated or destroyed.

This function is mostly useful to pass a byte array to a function that accepts a const char *.

Note: A QByteArray can store any byte values including '\0's, but most functions that take char * arguments assume that the data ends at the first '\0' they encounter.

int QByteArray::count () const

char * QByteArray::data ()

Returns a pointer to the data stored in the byte array. The pointer can be used to access and modify the bytes that compose the array. The data is '\0'-terminated, i.e. the number of bytes in the returned character string is size() + 1 for the '\0' terminator.

Returns a decoded copy of the hex encoded array hexEncoded. Input is not checked for validity; invalid characters in the input are skipped, enabling the decoding process to continue with subsequent characters.

Constructs a QByteArray that uses the first size bytes of the data array. The bytes are not copied. The QByteArray will contain the data pointer. The caller guarantees that data will not be deleted or modified as long as this QByteArray and any copies of it exist that have not been modified. In other words, because QByteArray is an implicitly shared class and the instance returned by this function contains the data pointer, the caller must not delete data or modify it directly as long as the returned QByteArray and any copies exist. However, QByteArray does not take ownership of data, so the QByteArray destructor will never delete the raw data, even when the last QByteArray referring to data is destroyed.

A subsequent attempt to modify the contents of the returned QByteArray or any copy made from it will cause it to create a deep copy of the data array before doing the modification. This ensures that the raw data array itself will never be modified by QByteArray.

Here is an example of how to read data using a QDataStream on raw data in memory without copying the raw data into a QByteArray:

Warning: A byte array created with fromRawData() is not null-terminated, unless the raw data contains a 0 character at position size. While that does not matter for QDataStream or functions like indexOf(), passing the byte array to a function accepting a const char * expected to be '\0'-terminated will fail.

If the QString contains non-ASCII Unicode characters, using this function can lead to loss of information. You can disable this function by defining QT_NO_CAST_TO_ASCII when you compile your applications. You then need to call QString::toAscii() (or QString::toLatin1() or QString::toUtf8() or QString::toLocal8Bit()) explicitly if you want to convert the data to const char *.

int QByteArray::indexOf ( const char * str, intfrom = 0 ) const

This is an overloaded function.

Returns the index position of the first occurrence of the string str in the byte array, searching forward from index position from. Returns -1 if str could not be found.

int QByteArray::indexOf ( charch, intfrom = 0 ) const

This is an overloaded function.

Returns the index position of the first occurrence of the character ch in the byte array, searching forward from index position from. Returns -1 if ch could not be found.

Inserts the string str at index position i in the byte array. The Unicode data is converted into 8-bit characters using QString::toAscii().

If i is greater than size(), the array is first extended using resize().

If the QString contains non-ASCII Unicode characters, using this function can lead to loss of information. You can disable this function by defining QT_NO_CAST_TO_ASCII when you compile your applications. You then need to call QString::toAscii() (or QString::toLatin1() or QString::toUtf8() or QString::toLocal8Bit()) explicitly if you want to convert the data to const char *.

QByteArray & QByteArray::insert ( inti, const char * str )

This is an overloaded function.

Inserts the string str at position i in the byte array.

If i is greater than size(), the array is first extended using resize().

QByteArray & QByteArray::insert ( inti, const char * str, intlen )

This is an overloaded function.

Inserts len bytes of the string str at position i in the byte array.

If i is greater than size(), the array is first extended using resize().

This function was introduced in Qt 4.6.

QByteArray & QByteArray::insert ( inti, charch )

This is an overloaded function.

Inserts character ch at index position i in the byte array. If i is greater than size(), the array is first extended using resize().

bool QByteArray::isNull () const

Qt makes a distinction between null byte arrays and empty byte arrays for historical reasons. For most applications, what matters is whether or not a byte array contains any data, and this can be determined using isEmpty().

Returns the index position of the last occurrence of the byte array ba in this byte array, searching backward from index position from. If from is -1 (the default), the search starts at the last byte. Returns -1 if ba could not be found.

Returns the index position of the last occurrence of the string str in the byte array, searching backward from index position from. If from is -1 (the default), the search starts at the last (size() - 1) byte. Returns -1 if str could not be found.

If the QString contains non-ASCII Unicode characters, using this function can lead to loss of information. You can disable this function by defining QT_NO_CAST_TO_ASCII when you compile your applications. You then need to call QString::toAscii() (or QString::toLatin1() or QString::toUtf8() or QString::toLocal8Bit()) explicitly if you want to convert the data to const char *.

int QByteArray::lastIndexOf ( const char * str, intfrom = -1 ) const

This is an overloaded function.

Returns the index position of the last occurrence of the string str in the byte array, searching backward from index position from. If from is -1 (the default), the search starts at the last (size() - 1) byte. Returns -1 if str could not be found.

int QByteArray::lastIndexOf ( charch, intfrom = -1 ) const

This is an overloaded function.

Returns the index position of the last occurrence of character ch in the byte array, searching backward from index position from. If from is -1 (the default), the search starts at the last (size() - 1) byte. Returns -1 if ch could not be found.

Note: QByteArray is an implicitly shared class. Consequently, if this is an empty QByteArray, then this will just share the data held in ba. In this case, no copying of data is done, taking constant time. If a shared instance is modified, it will be copied (copy-on-write), taking linear time.

If this is not an empty QByteArray, a deep copy of the data is performed, taking linear time.

Replaces every occurrence of the string before with the string after. Since the sizes of the strings are given by bsize and asize, they may contain zero characters and do not need to be zero-terminated.

Replaces every occurrence of the string before with the byte array after. The Unicode data is converted into 8-bit characters using QString::toAscii().

If the QString contains non-ASCII Unicode characters, using this function can lead to loss of information. You can disable this function by defining QT_NO_CAST_TO_ASCII when you compile your applications. You then need to call QString::toAscii() (or QString::toLatin1() or QString::toUtf8() or QString::toLocal8Bit()) explicitly if you want to convert the data to const char *.

Replaces every occurrence of the character before with the string after. The Unicode data is converted into 8-bit characters using QString::toAscii().

If the QString contains non-ASCII Unicode characters, using this function can lead to loss of information. You can disable this function by defining QT_NO_CAST_TO_ASCII when you compile your applications. You then need to call QString::toAscii() (or QString::toLatin1() or QString::toUtf8() or QString::toLocal8Bit()) explicitly if you want to convert the data to const char *.

QByteArray & QByteArray::replace ( charbefore, const char * after )

This is an overloaded function.

Replaces every occurrence of the character before with the string after.

QByteArray & QByteArray::replace ( charbefore, charafter )

This is an overloaded function.

Replaces every occurrence of the character before with the character after.

void QByteArray::reserve ( intsize )

Attempts to allocate memory for at least size bytes. If you know in advance how large the byte array will be, you can call this function, and if you call resize() often you are likely to get better performance. If size is an underestimate, the worst that will happen is that the QByteArray will be a bit slower.

The sole purpose of this function is to provide a means of fine tuning QByteArray's memory usage. In general, you will rarely ever need to call this function. If you want to change the size of the byte array, call resize().

QByteArray & QByteArray::setRawData ( const char * data, uintsize )

Resets the QByteArray to use the first size bytes of the data array. The bytes are not copied. The QByteArray will contain the data pointer. The caller guarantees that data will not be deleted or modified as long as this QByteArray and any copies of it exist that have not been modified.

This function can be used instead of fromRawData() to re-use existings QByteArray objects to save memory re-allocations.

int QByteArray::size () const

Returns the number of bytes in this byte array.

The last byte in the byte array is at position size() - 1. In addition, QByteArray ensures that the byte at position size() is always '\0', so that you can use the return value of data() and constData() as arguments to functions that expect '\0'-terminated strings. If the QByteArray object was created from a raw data that didn't include the trailing null-termination character then QByteArray doesn't add it automaticall unless the deep copy is created.

Splits the byte array into subarrays wherever sep occurs, and returns the list of those arrays. If sep does not match anywhere in the byte array, split() returns a single-element list containing this byte array.

void QByteArray::squeeze ()

Releases any memory not required to store the array's data.

The sole purpose of this function is to provide a means of fine tuning QByteArray's memory usage. In general, you will rarely ever need to call this function.

QByteArray QByteArray::toHex () const

int QByteArray::toInt ( bool * ok = 0, intbase = 10 ) const

Returns the byte array converted to an int using base base, which is 10 by default and must be between 2 and 36, or 0.

If base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.

Returns 0 if the conversion fails.

If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.

long QByteArray::toLong ( bool * ok = 0, intbase = 10 ) const

Returns the byte array converted to a long int using base base, which is 10 by default and must be between 2 and 36, or 0.

If base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.

Returns 0 if the conversion fails.

If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.

Returns the byte array converted to a long long using base base, which is 10 by default and must be between 2 and 36, or 0.

If base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.

Returns 0 if the conversion fails.

If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.

Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.

short QByteArray::toShort ( bool * ok = 0, intbase = 10 ) const

Returns the byte array converted to a short using base base, which is 10 by default and must be between 2 and 36, or 0.

If base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.

Returns 0 if the conversion fails.

If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.

Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.

uint QByteArray::toUInt ( bool * ok = 0, intbase = 10 ) const

Returns the byte array converted to an unsigned int using base base, which is 10 by default and must be between 2 and 36, or 0.

If base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.

Returns 0 if the conversion fails.

If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.

Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.

ulong QByteArray::toULong ( bool * ok = 0, intbase = 10 ) const

Returns the byte array converted to an unsigned long int using base base, which is 10 by default and must be between 2 and 36, or 0.

If base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.

Returns 0 if the conversion fails.

If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.

Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.

Returns the byte array converted to an unsigned long long using base base, which is 10 by default and must be between 2 and 36, or 0.

If base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.

Returns 0 if the conversion fails.

If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.

Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.

ushort QByteArray::toUShort ( bool * ok = 0, intbase = 10 ) const

Returns the byte array converted to an unsigned short using base base, which is 10 by default and must be between 2 and 36, or 0.

If base is 0, the base is determined automatically using the following rules: If the byte array begins with "0x", it is assumed to be hexadecimal; if it begins with "0", it is assumed to be octal; otherwise it is assumed to be decimal.

Returns 0 if the conversion fails.

If ok is not 0: if a conversion error occurs, *ok is set to false; otherwise *ok is set to true.

Note: The conversion of the number is performed in the default C locale, irrespective of the user's locale.

QByteArray::operator const char * () const

Returns a pointer to the data stored in the byte array. The pointer can be used to access the bytes that compose the array. The data is '\0'-terminated. The pointer remains valid as long as the array isn't reallocated or destroyed.

This operator is mostly useful to pass a byte array to a function that accepts a const char *.

You can disable this operator by defining QT_NO_CAST_FROM_BYTEARRAY when you compile your applications.

Note: A QByteArray can store any byte values including '\0's, but most functions that take char * arguments assume that the data ends at the first '\0' they encounter.

QByteArray::operator const void * () const

Returns a pointer to the data stored in the byte array. The pointer can be used to access the bytes that compose the array. The data is '\0'-terminated. The pointer remains valid as long as the array isn't reallocated or destroyed.

This operator is mostly useful to pass a byte array to a function that accepts a const char *.

You can disable this operator by defining QT_NO_CAST_FROM_BYTEARRAY when you compile your applications.

Note: A QByteArray can store any byte values including '\0's, but most functions that take char * arguments assume that the data ends at the first '\0' they encounter.

QByteArray & QByteArray::operator+= ( const QByteArray & ba )

Note: QByteArray is an implicitly shared class. Consequently, if this is an empty QByteArray, then this will just share the data held in ba. In this case, no copying of data is done, taking constant time. If a shared instance is modified, it will be copied (copy-on-write), taking linear time.

If this is not an empty QByteArray, a deep copy of the data is performed, taking linear time.

This operation typically does not suffer from allocation overhead, because QByteArray preallocates extra space at the end of the data so that it may grow without reallocating for each append operation.

Appends the string str onto the end of this byte array and returns a reference to this byte array. The Unicode data is converted into 8-bit characters using QString::toAscii().

If the QString contains non-ASCII Unicode characters, using this operator can lead to loss of information. You can disable this operator by defining QT_NO_CAST_TO_ASCII when you compile your applications. You then need to call QString::toAscii() (or QString::toLatin1() or QString::toUtf8() or QString::toLocal8Bit()) explicitly if you want to convert the data to const char *.

QByteArray & QByteArray::operator+= ( const char * str )

This is an overloaded function.

Appends the string str onto the end of this byte array and returns a reference to this byte array.

QByteArray & QByteArray::operator+= ( charch )

This is an overloaded function.

Appends the character ch onto the end of this byte array and returns a reference to this byte array.

The return value is of type QByteRef, a helper class for QByteArray. When you get an object of type QByteRef, you can use it as if it were a char &. If you assign to it, the assignment will apply to the character in the QByteArray from which you got the reference.

Compresses the data byte array and returns the compressed data in a new byte array.

The compressionLevel parameter specifies how much compression should be used. Valid values are between 0 and 9, with 9 corresponding to the greatest compression (i.e. smaller compressed data) at the cost of using a slower algorithm. Smaller values (8, 7, ..., 1) provide successively less compression at slightly faster speeds. The value 0 corresponds to no compression at all. The default value is -1, which specifies zlib's default compression.

QByteArrayqUncompress ( const QByteArray & data )

This function will uncompress data compressed with qCompress() from this and any earlier Qt version, back to Qt 3.1 when this feature was added.

Note: If you want to use this function to uncompress external data that was compressed using zlib, you first need to prepend a four byte header to the byte array containing the data. The header must contain the expected length (in bytes) of the uncompressed data, expressed as an unsigned, big-endian, 32-bit integer.

char * qstrncpy ( char * dst, const char * src, uintlen )

A safe strncpy() function.

Copies at most len bytes from src (stopping at len or the terminating '\0' whichever comes first) into dst and returns a pointer to dst. Guarantees that dst is '\0'-terminated. If src or dst is 0, returns 0 immediately.

This function assumes that dst is at least len characters long.

Note: When compiling with Visual C++ compiler version 14.00 (Visual C++ 2005) or later, internally the function strncpy_s will be used.

1. Download the tools

Before you start developing, you'll need to visit the Downloads tab. Here you'll find downloads for the BlackBerry 10 Native SDK, BlackBerry 10 Device Simulator, and some other useful tools.

2. Try the sample apps

Now featuring a filter control, the Sample apps tab allows you to search for samples by name or by feature.

Select either the Core or Cascades radio buttons to display the samples relevant to you.

3. Educate yourself

The Documentation tab contains tons of examples, tutorials, and best practices to guide you along the path towards building an awesome app.

You can access all the documentation that you need in the left-hand navigation.

4. Start developing

The Reference tab is where you'll find essential details about how to use our APIs.

You can use the left-hand navigation to choose how you would like to browse the reference: by module, by topic, or alphabetically. If you have an idea of what you are looking for, start typing it in the Filter box.